1. Field of the Invention
The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device and a method of driving the same, which compensate for a characteristic change of a driving transistor to enhance a luminance uniformity of an image.
2. Discussion of the Related Art
Recently, with the advancement of multimedia, the importance of flat panel display (FPD) devices is increasing. Therefore, various FPD devices such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, and organic light emitting display devices are being commercialized.
In such FPD devices, the organic light emitting display devices display an image by using an organic light emitting element that emits light by a recombination of an electron and a hole. The organic light emitting display devices have a fast response time and have no limitation in a viewing angle because self-emitting light, and thus are attracting much attention as next generation FPD devices.
One pixel of a general organic light emitting display device includes a pixel circuit that includes an organic light emitting element and a driving transistor that drives the organic light emitting element. However, in the general organic light emitting display device, threshold voltages/mobility characteristics of driving transistors of a plurality of pixels differ due to a driving time and a non-uniformity of a manufacturing process of a thin film transistor (TFT), and thus, despite the same data voltage being applied to the pixels, amounts of current flowing in the driving transistors of the pixels differ. A current deviation between the driving transistors of the pixels causes a luminance deviation between the pixels, causing a reduction in uniformity of an image quality. As methods for solving such problems, Korean Patent Publication No. 10-2010-0047505 (hereinafter referred to as patent document 1), Korean Patent Publication No. 10-2011-0066506 (hereinafter referred to as patent document 2), and Korean Patent Registration No. 10-1073226 (hereinafter referred to as patent document 3) are disclosed.
In the reference documents, a sensing transistor and a sensing line are formed in each pixel. An analog-to-converter (ADC) of a sensing unit included in a data driver (i.e., a data driving integrated circuit (IC)) senses a voltage charged into the sensing line according to driving of the driving transistor, and a characteristic change of the driving transistor is compensated for by correcting data according to the sensed voltage, thereby preventing a quality of an image from being degraded due to a luminance deviation between the pixels.
However, the ADC generally has a gain error and an offset error, and a deviation of output data output from the ADC occurs due to a process differential between a plurality of the data driving ICs in a manufacturing process of the data driving ICs. In addition, a deviation between the ADCs of the data driving ICs also occurs.
The gain error denotes an error in which an actual digital output deviates by a certain rate from an ideal digital output with respect to an analog input, and in detail, the gain error is an error that occurs when an accurate value at the center of an analog input range approaches the minimum value and maximum value of the analog input range.
The offset error denotes an error in which an actual digital output deviates by a certain amount from an ideal digital output with respect to an analog input, and in detail, the offset error denotes a high or low degree of a measurement value which is obtained when measuring a signal known to a user.
FIG. 1 is a waveform diagram showing output data with respect to an input voltage of an analog-to-digital converter (ADC). FIG. 2 is a waveform diagram for describing an output deviation between a plurality of data driving ICs in a general organic light emitting display device.
In FIG. 1, a graph A is a graph that shows ideal output data with respect to an input voltage, and a graph B is a graph that shows actual output data with respect to the input voltage.
As seen in FIG. 1, even when the same input voltage is applied to the ADC, a deviation of output data of the ADC occurs. That is, as shown in the graph A, ideal output data of the ADC with no gain error and offset error is determined by a multiplication (x) of an input voltage (x) and an ideal gain error (a). However, the ADC generally has the gain error and the offset error, and thus, as shown in the graph B, actual output data of the ADC is determined by the sum of a value (x×a′), which is obtained by multiplying the input voltage (x) and an actual gain error (b), and the actual offset error (i.e., an output with respect to an input voltage of 0).
As seen in FIG. 2, it can be seen that an output deviation between a plurality of the ADCs occurs even between a plurality of data driving ICs (D-IC #1 to #8).
Therefore, the reference documents correct data on the basis of sensing data which are distorted due to a deviation of the sensing data of the ADCs, and thus cannot more accurately compensate for the characteristic changes of the driving transistors.
As a result, it is required to minimize an output deviation between the ADCs that respectively sense the characteristic changes of the driving transistors.